Association of zygotic piRNAs derived from paternal elements with hybrid dysgenesis in .

BACKGROUND

-element transposition in the genome causes P-M hybrid dysgenesis in . Maternally deposited piRNAs suppress -element transposition in the progeny, linking them to P-M phenotypes; however, the role of zygotic piRNAs derived from paternal elements is poorly understood.

RESULTS

To elucidate the molecular basis of -element suppression by zygotic factors, we investigated the genomic constitution and -element piRNA production derived from fathers. As a result, we characterized males of naturally derived Q, M' and P strains, which show different capacities for the -element mobilizations introduced after hybridizations with M-strain females. The amounts of piRNAs produced in ovaries of F1 hybrids varied among the strains and were influenced by the characteristics of the piRNA clusters that harbored the elements. Importantly, while both the Q- and M'-strain fathers restrict the -element mobilization in ovaries of their daughters, the Q-strain fathers supported the production of the highest piRNA expression in the ovaries of their daughters, and the M' strain carries elements in transcriptionally active regions directing the highest expression of elements in their daughters. Interestingly, the zygotic -element piRNAs, but not the element mRNA, contributed to the variations in transposition immunity in the granddaughters.

CONCLUSIONS

The piRNA-cluster-embedded elements and the transcriptionally active elements from the paternal genome are both important suppressors of element activities that are co-inherited by the progeny. Expression levels of the -element piRNA and -element mRNA vary among F1 progeny due to the constitution of the paternal genome, and are involved in phenotypic variation in the subsequent generation.